In the image “C” is the value for level:ref, level would be 1. level:ref=C could be “Ground floor”, “1st floor”, “2nd floor”, etc, depending on how it’s signed in the building. In OSM, level for that floor is always 1. The building’s entrance could be on C or D.
Questions:
Obviously, you could add both tags, but if you had to pick just one, which one would it be?
If you get “level”: how would you find the defibrillator in the building?
If you’d have to fill the information for a building that isn’t mapped in OSM, how would you determine level?
If the defibrillator is inside the building, and the building has multiple levels, I think you have to map it with level if you want to map its actual location and not just the fact that the building itself has a defibrillator somewhere. level is how you tell data consumers what floor something is on, level:ref is just additional descriptive info for humans.
I use an app that shows indoor maps or otherwise translates OSM tags into useful human-readable output
I don’t speak the local language, so the level names contain unfamiliar words or characters
level:ref isn’t prominently signed on the ground, and only exists because the mapper paid close attention to less-obvious sources such as as room numbers or elevator buttons.
level:ref seems more helpful if:
I use a simple app which just shows me the raw OSM values and I have to make sense of them myself
I live in a part of the world that traditionally numbers the ground floor as “1”, making OSM’s 0-based standard for level more confusing to me
The level names are actually prominently signed inside the building.
I think you can use level:ref for the same. It’s the value you will find in the elevator.
At least in the area I map, we tend to have hardly any indoor mapping around the defibrillators, nor is there an app that uses indoor mapping, but all buildings are mapped. Sometimes not even the business where the defibrillator is located is mapped.
Just knowing the floor of the building on it’s own may not be particularly helpful in finding the Defib in an emergency. If that’s what you’re most interested in, I’d suggest populating the human-readable defibrillator:location=* with something suitable (e.g. “In the Acme Corp office building, on the 5th floor, next to main elevators.”) would be the best thing to do.
For OSM mapping and data users, level=* is probably more useful, since it’s more likely to be also tagged on surrounding objects for anyone wanting to make floor plans.
For applications like 3D-Rendering level is required, but in an emergency it’s most likely that level:ref - if that corresponds to the numbering/reference used on site - is more helpful or as already said defibrillator:location=* or even description=*.
When adding things like this in many cases level and level:ref are known and if that’s the case I would add both (if they aren’t the same).
level is used by map drawing software to order the levels in the correct physical order, and can be used for indoor routing. Typically this is internal to the software and not displayed to users of a map.
level:ref is used to provide a reference that matches the signage within the building for easier wayfinding. Typically this is what is displayed to users of a map.
For most purposes it’s best to tag both (even if they are the same).
If you get “level”: how would you find the defibrillator in the building?
Via description or such similar tag – StreetComplete et al, already have a task for filling that information with a descriptive, human-oriented text (“from the parking entrance, the third column to the left”). I see no purpose in twirling hairs over a machine-oriented resolution.
if you had to pick just one, which one would it be?
level, of course. It’s the one that’s already available and established. If I’m querying OSM to find a defibrilator, instead of speaking to the human operator in charge, then I am already expecting that it counts the floors as 0-based.
